Opened up the engine, looky what I found
Moderators: oldjapanesebikes, H2RICK, diamondj, Suzsmokeyallan
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- To the on ramp
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- Location: Cedar Rapids, Iowa
Opened up the engine, looky what I found
What I found was really fat jetting but tell me, it seems that it may not be inappropriate.
Anyway, in getting ready to re-jet my carbs and install my shaved head I tore the top end down last night. I also wanted to verify the bore size and check on any port chamfering etc....
First up the bike ran pretty good before (I hope it does after also) claimed to be on a fairly recent .5mm overbore, and opened up airbox as the only mods. I don't know for sure but it kind of looks like the carbs may have been bored or honed.
Since I am installing the Jemcos I pulled the carb rack to verify my jet sizes. What I found was
25 pilots all the way across
117 mains in the left and right
112 main in the center
I forgot to pull the needles yet
Seems like really big main jets but here is a pic of the plugs (they look pretty good
Also the cylinder tops
Left
right
center
Stock cylinder head
Looks like the jetting is acceptable? It kind of surprised me since all of the specs I have read claims some smaller mains.
Here is the spare head I got and want to try out
I need to jet the carbs for the following mods:
Jemco Pipes
Head skim
Uni Filter pods
What say ye? Go up 1 or two on the pilot? Then run 117's all the way across or should I go even larger on the mains? From the plug read is it too rich? Those mains sizes seem right for a modified 750 LOL!!
Jason
Anyway, in getting ready to re-jet my carbs and install my shaved head I tore the top end down last night. I also wanted to verify the bore size and check on any port chamfering etc....
First up the bike ran pretty good before (I hope it does after also) claimed to be on a fairly recent .5mm overbore, and opened up airbox as the only mods. I don't know for sure but it kind of looks like the carbs may have been bored or honed.
Since I am installing the Jemcos I pulled the carb rack to verify my jet sizes. What I found was
25 pilots all the way across
117 mains in the left and right
112 main in the center
I forgot to pull the needles yet
Seems like really big main jets but here is a pic of the plugs (they look pretty good
Also the cylinder tops
Left
right
center
Stock cylinder head
Looks like the jetting is acceptable? It kind of surprised me since all of the specs I have read claims some smaller mains.
Here is the spare head I got and want to try out
I need to jet the carbs for the following mods:
Jemco Pipes
Head skim
Uni Filter pods
What say ye? Go up 1 or two on the pilot? Then run 117's all the way across or should I go even larger on the mains? From the plug read is it too rich? Those mains sizes seem right for a modified 750 LOL!!
Jason
- H2RICK
- AMA Superbike
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- Joined: Sun Oct 19, 2008 11:07 am
- Country: CANADA
- Suzuki 2-Strokes: GT550A, GSF1200SK6 currently
- Location: Cowtown aka Calgary, Canada
I don't know how many miles are on that new top end but it looks like 5 or 6 thousand at least. If it isn't AT LEAST that many miles, then STOP using the injector oil that's in the bike. There are 'waaaayyyyyy too many non-combustibles in that oil from looking at your pics. Try a full synthetic to stop the crud buildup.
As to jetting: The jets that WERE in it as per your post 117.5 - 112.5 - 117.5 have too small a centre jet. There should be only ONE jet size difference between them, so the centre jet SHOULD have been a 115.
You should probably order: First set= 2 of #122.5 and 1 of #120
Second set= 2 of #125 and you can use 1 of the #122.5 from the First set in the centre cylinder for this set.
Set your needles on the rich side, which means put the clip in the fourth groove from the TOP of the needle.
Then you can start reading plugs. I would put the Second set of jets in first.
You can always put the leaner set in if required.....but you can't weld up a hole in your piston crown if you put the leaner set in first....if ya get my drift.
As to jetting: The jets that WERE in it as per your post 117.5 - 112.5 - 117.5 have too small a centre jet. There should be only ONE jet size difference between them, so the centre jet SHOULD have been a 115.
You should probably order: First set= 2 of #122.5 and 1 of #120
Second set= 2 of #125 and you can use 1 of the #122.5 from the First set in the centre cylinder for this set.
Set your needles on the rich side, which means put the clip in the fourth groove from the TOP of the needle.
Then you can start reading plugs. I would put the Second set of jets in first.
You can always put the leaner set in if required.....but you can't weld up a hole in your piston crown if you put the leaner set in first....if ya get my drift.
GT550A Mint & Original
H2A Semi-Hot Rod Built From A Basket Case
KZ650C2 Mint & Original...mostly
GSF1200SK6 Bandit...My LD Ride
Additional H2 projects In Boxes.....
MBD Sufferer
H2A Semi-Hot Rod Built From A Basket Case
KZ650C2 Mint & Original...mostly
GSF1200SK6 Bandit...My LD Ride
Additional H2 projects In Boxes.....
MBD Sufferer
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- To the on ramp
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- Joined: Sun Oct 19, 2008 4:44 pm
- Location: Cedar Rapids, Iowa
Yeah it's got some miles on it. I tried to find out more details on exactly what was going on with this bike after I bought it. I even talked to 2 previous owners. When I was talking to the guy that did most of the work on the thing he was an older gentleman and was having some difficulty remembering all of the details of what I was asking him.
I have discontinued used of the previous oil. It was told to me that it was some sort of outboard motor oil.
I have discontinued used of the previous oil. It was told to me that it was some sort of outboard motor oil.
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- Expert racer
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- Joined: Mon Dec 01, 2008 2:52 am
- Location: Manchester, UK
I'd say that looks pretty good, and some decent 2 stroke oil will help keep it that way.
One tip I can recommend is using the NGK platinum plugs (EVX). You can order them pretty cheap online, and they simply never seem to need cleaning or gapping. Just set the gap to 0.7mm and forget them.
Every little helps, especially if you're running the stock points ignition.
One tip I can recommend is using the NGK platinum plugs (EVX). You can order them pretty cheap online, and they simply never seem to need cleaning or gapping. Just set the gap to 0.7mm and forget them.
Every little helps, especially if you're running the stock points ignition.
1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed
- Triplerocky
- On the main road
- Posts: 138
- Joined: Tue Oct 21, 2008 2:42 pm
- Country: Italy
- Suzuki 2-Strokes: gt380m, gt380a, ts400b
- Location: Heel Of Italy
those jets seems really huge for a stock 380.... it comes with a #80-80-80 main jet set (round/button/reverse type), O-2 needle jet, 4DH7 jet needle at 2° notch from the top; from the very last 1977 parts list and applicable to the L,M,A,B model. My 380 (really 399 cc.) got #82,5 mains, no other changes, runs very well with clean and light tan plugs.
What carbs are mounted on yours to carry on such BIG mains?
What carbs are mounted on yours to carry on such BIG mains?
'75 GT380M
'77 GT380B
'77 TS400B
('74 GT380 is gone at 2300 euros)
'77 GT380B
'77 TS400B
('74 GT380 is gone at 2300 euros)
- Triplerocky
- On the main road
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- Joined: Tue Oct 21, 2008 2:42 pm
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- Suzuki 2-Strokes: gt380m, gt380a, ts400b
- Location: Heel Of Italy
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- To the on ramp
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- Location: Cedar Rapids, Iowa
After I got my shaved head home last night I was a little concerned with it.
I took it to a very reputable machinist and he had to charge me extra when I picked it up. Turns out that he said the head had a little bit of twist or warp to it, so it took more set up time than he quoted me originally.
Upon my home inspection I am thinking maybe the combustion chamber volumes were not ok because of the difference in the visible ridge around the chamber. It looked like the head was cut deeper in the middle than on the outer chambers.
So I start stressing a little because I am thinking maybe I wasted money and ruined a good part.
The only thing left to do is measure it somehow. I called up my Dad who works on Sprts cars and I ended up CCing the head last night. I was able to use good old Dad's CCing kit. Silly me I forgot to bring the stock head for comparison.
However I am super happy to report that through my imperfect method of measuring the volume (I am sure I lost a drip here or there) All of the combustion chambers measured within .5cc of each other. Right at about 21CC
Tonight I will bolt the modified and the stock head on and take a compression reading for each one. I can't wait to find out the results!!
I took it to a very reputable machinist and he had to charge me extra when I picked it up. Turns out that he said the head had a little bit of twist or warp to it, so it took more set up time than he quoted me originally.
Upon my home inspection I am thinking maybe the combustion chamber volumes were not ok because of the difference in the visible ridge around the chamber. It looked like the head was cut deeper in the middle than on the outer chambers.
So I start stressing a little because I am thinking maybe I wasted money and ruined a good part.
The only thing left to do is measure it somehow. I called up my Dad who works on Sprts cars and I ended up CCing the head last night. I was able to use good old Dad's CCing kit. Silly me I forgot to bring the stock head for comparison.
However I am super happy to report that through my imperfect method of measuring the volume (I am sure I lost a drip here or there) All of the combustion chambers measured within .5cc of each other. Right at about 21CC
Tonight I will bolt the modified and the stock head on and take a compression reading for each one. I can't wait to find out the results!!
- oldjapanesebikes
- Moto GP
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- Suzuki 2-Strokes: GT750(Jx3,L,M,A,B),T500
- Location: Ontario
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- oldjapanesebikes
- Moto GP
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- Suzuki 2-Strokes: GT750(Jx3,L,M,A,B),T500
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I've thought of doing this a couple of times, but never actually got round to it - how exactly did you do the measurement ? Eyedropper ?jaybob wrote: The only thing left to do is measure it somehow. I called up my Dad who works on Sprts cars and I ended up CCing the head last night. I was able to use good old Dad's CCing kit.
Ian
If at first you don't succeed, just get a bigger hammer !
If at first you don't succeed, just get a bigger hammer !
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- Yeah Man, the Interstate
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oldjapanesebikes wrote:I've thought of doing this a couple of times, but never actually got round to it - how exactly did you do the measurement ? Eyedropper ?jaybob wrote: I was able to use good old Dad's CCing kit.
We propped the head upside down and level.
Installed a sparkplug in the hole.
Ran a bead of grease around the edge of the chamber
Layed down a piece of glass with a small hole in it over the chamber and sealed it with the grease
Then we used a long graduated cylinder mounted on a stand
We placed the cylinder over the hole in the glass
Filled up the cylinder with about 50cc of liquid and wrote down the starting fluid level
Using a valve on the end of the cylinder we slowly filled up the chamber
When the chamber was full we wrote down the ending fluid level and then subtracted the difference for the volume.
We used dyed alcahol for the fluid since it does not have the surface tension and meniscus that water does.
I should have snapped a pic but forgot. Maybe when I do my stock head I will remember.